Machines for manufacturing round wooden frames are known in the prior art and they comprise a base frame on which a feeding bench and a circular pattern are mounted. A continuous thin wooden strip is wound around the revolving pattern until a rough frame of the desired thickness is obtained. This rough frame is then sent on to subsequent finishing operations.
As the extraction of the rough frame from the pattern is made possible in the prior art by the radial contraction of the pattern, the latter is generally formed as a cylinder from a thin metal plate, open along a generating line and fixed to a central hub. The cylindrical surface of this pattern is resiliently contracted, in the resting condition, and is expanded prior to the winding of the thin wooden strip, either by extending the rods connecting the surface to the hub, or by frontally applying circular discs having a conical profile.
While such known machines successfully produce circular one piece wooden frames, they possess certain drawbacks and limitations, among which are:
(1) The fact that it is difficult to manufacture very thick frames. In fact, the wide variation in distance between the axis of the revolving pattern and the point of tangency of the wooden strip therewith, causes undesired bending of the strip and possible breaking of the same.
(2) The fact that the resiliency of the cylindrical pattern is concentrated on a short section of its side surface. This involves the transmission of high dynamic stresses to the rods connected with the hub, and the possible loss of a perfect cylindrical shape during the expansion of the pattern. Moreover, the known machines cannot satisfactorily produce oval frames instead of round ones.
(3) During strip winding, the wooden strip is submitted to continuous bendings, due to variations in the distance between the point of tangency and the axis of the revolving pattern, with the resulting possibility of breaking the strip.
(4) To maintain the oval configuration of the pattern, when expanding the latter, it is necessary to use discs having a conical profile. The manufacturing of such discs is expensive and laborious.
The above deficiencies become even greater if the curvilinear frame being produced requires a shape different from cylindrical or from oval. With the prior art drawbacks in mind, the present invention seeks to provide a machine for efficiently manufacturing convex wooden frames of any required thickness and any curvilinear convex shape.
Other features and advantages of the invention will become apparent during the course of the following detailed description.